In the field of numerically controlled industrial machinery such as machine tools and robots, conventionally, a mode in which an image relating to a movable structure such as a tool rest, a spindle head and a robot arm is displayed on a screen of a display apparatus has been adopted, and, by viewing this displayed image, an operator can recognize the operation state of the movable body without viewing the movable structure directly with his eyes.
As such an apparatus for displaying an image of a movable structure, a numerical controller as disclosed in the Patent Literature 1 mentioned below has conventionally been suggested. This numerical controller includes a video camera installed in the inside of a machine tool, display image generating means which, using video image data captured by the video camera and internal data of the numerical controller, generates display image data in which character information is superimposed on a video image, and a device for displaying the display image data.
According to this numerical controller, images of a workpiece and a tool during machining are captured by the video camera, display image data in which character information (a coordinate position of a tool cutting edge) is superimposed on a video image is generated by the display image generating means, and images relating to the generated display image data are displayed by the display apparatus. Besides, by arranging the position of display of the character information in the vicinity of the position related to the character information on the video image, the amount of movement of an operator's line of sight between the video image and the character information at the time of visually recognizing these display images are reduced.